“PDF document” is a widely used electronic document. “PDF” is the acronym for “Portable Document Format” and is a format for electronic documents. All the documents in “PDF” format are known as PDF documents.
The PDF document is usually used for converting from a paper document. The process of converting is as follows: firstly scanning the content of the paper document into an electronic image document, and then transforming the data of the electronic image document into a PDF document by means of software(s). Because the electronic image document scanned from the paper document may carry a certain amount of impurity data (i.e., the data not belonging to the original paper document but coming from the scanning process), the impurity data is retained during the process of converting in format and seriously affecting the reading experiences of readers. And then, the clarity of the PDF document converted in the prior art is poor, and the reading experiences of readers are also poor. Therefore, it is easy to damage the eyes of the readers especially when you read them on the small screen of electronic devices (such as mobile phones).